When using k-fold cross-validation with k=5, how many times is each observation used for validation?
Select an answer to reveal the explanation.
Short Explanation and Infographic
Here's the deal — c is correct because in k-fold CV, each observation belongs to exactly one fold and is used for validation only when its fold is held out, which happens exactly once. A is wrong; each observation is in the validation set only once.
Full explanation below image
Full Explanation
C is correct because in k-fold CV, each observation belongs to exactly one fold and is used for validation only when its fold is held out, which happens exactly once. A is wrong; each observation is in the validation set only once. B and D describe how many times each observation is in the training set (k-1 = 4 times), not the validation set.